1. Field of the Invention
The present invention relates to the drilling and production of fluids from petroleum wells. More particularly, the present invention relates to an apparatus for straining solid particulates from well fluids prior to their passage through a hydraulic choke.
2. Description of the Related Art
Hydraulic choke devices are commonly used in the oilfield when drilling or treating wells. Herein, the term “hydraulic choke” is taken to refer to the fact that the device is used with a variety of fluids, such as drilling mud, salt water, oil, gas, and other chemicals which may flow into or out from the well. “Hydraulic” does not herein refer to the choke actuation means. The hydraulic choke is utilized as a pressure-reducing valve for fluids flowing out of a well. The pressure of fluids emerging from a well flow control system must be reduced substantially in order to further process and store those fluids. A typical problem arising during operation of a hydraulic choke is a tendency for relatively large solid particulate matter to restrict or plug the choke, so that the choke's flow control becomes irregular. The particulate matter causing problems can be drill cuttings, spalled segments of the downhole geologic formations, or debris from the drilling equipment. Conventional chokes are run without any screening of the fluid or other filtering of the well fluids.
Strainer screens are routinely used to remove large particulates from the outflow stream of wells, but, except for small in-line screens, this screening is done at atmospheric pressure on vibrating screens termed shale shakers for drilling. If a significant amount of particulate matter is present or flow is sustained over a long period, then a fixed screen device will become plugged and reduce fluid flow. In such a case, the plugged screen itself can structurally fail and add to the particulate matter in the flow stream.
Hydrocyclones are also used to separate heavier components, such as rock cuttings and metallic debris, from the outflowing fluid stream. However, such particulate removal systems are used at very low system pressures. Furthermore, hydrocyclones typically will not separate particulates having relatively low specific gravities, such as rubber.
A system is needed to control the size of particles in the well fluid that passes through the piping upstream of the choke. There is also a need for a reliable means of removing particulate material from the outflow stream of a well so that strainer plugging by excessive particulate entrapment can be identified and remedied without interrupting the flow of the well. The means must be useable at very high pressures upstream of the hydraulic choke so that it can serve to protect the choke from clogging and flow damage accentuation resulting from particle entrapment in the choke.